An Irish nanny accused of beating a one-year-old girl who later died has pleaded not guilty to murder.

Aisling Brady McCarthy is also facing charges of assaulting Rehma Sabir on her first birthday, at the baby's home in Cambridge, Massachusetts earlier this year.

The nanny, who has been living in America illegally since 2002, had the charges upgraded on Thursday and will appear in court again on May 9.

The 34-year-old, who was refused bail, is facing charges of first degree murder and for allegedly violently injuring the baby, causing her death.

Court records previously revealed that a blood-stained pillow, blanket and baby wipes were found in Rehma's bedroom after emergency services were called to the home on January 14.

Official reports said a post-mortem found that Rehma's death was caused by blunt force head injuries which were not accidental.

Records from the latest hearing stated that Cambridge Police responded to a report of an unresponsive infant at the home and found baby Rehma breathing but unconscious.

Police photograph of Aisling McCarthy Brady

She was taken to the Children's Hospital in Boston suffering from brain damage including subdural and retinal haemorrhaging and cerebral swelling.

The youngster was pronounced dead on January 16.

Court records also stated that the police investigation, including witness statements, showed Brady McCarthy, who had been living in the Quincy area south of Boston, was in sole care of Rehma on January 14.

Police also alleged the nanny was the only person in contact with Rehma when she sustained abusive head trauma injuries that caused her death.

Brady McCarthy had been employed as a nanny by entrepreneur Sameer Sabir, the baby's father, and his wife Nada Siddiqui, who is originally from Karachi, Pakistan.

The couple had moved from London to the US.

The nanny worked for them for six months until their baby's death.

Investigators who interviewed Brady said she told them the baby seemed "her usual self" on the morning of the alleged assault.

She told them that in the afternoon she put Rehma in her crib, believing she was tired, but three hours later returned to find her "clenching her fists and her arms and legs were stiff".

Around that time Ms Siddiqui returned home and called police.

Brady McCarthy's lawyer, Melinda Thompson, claimed after the arrest that her client had no role in the baby's death.